/in/foo.c: In function 'main':
/in/foo.c:8:14: warning: implicit declaration of function 'sum' [-Wimplicit-function-declaration]
  printf("%d",sum(c(n,m)));
              ^~~
/in/foo.c:8:18: warning: implicit declaration of function 'c' [-Wimplicit-function-declaration]
  printf("%d",sum(c(n,m)));
                  ^
/in/foo.c:5:13: warning: unused variable 'cout' [-Wunused-variable]
     int n,m,cout;
             ^~~~